not sure if either marsh or willow tit
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A recent study has found that the best features to use to identify Marsh Tit are the presence of a pale spot on the edge of the upper mandible of the bill (below the nostrils), and the contrast between the white ear coverts and buff/brownish rear cheeks - both of which are visible if you enlarge the photo here. Willow Tits lack the pale spot on the bill and the ear coverts/cheeks are white in colour (at most with a pale greyish-buff wash on the rear cheeks. The lack of a pale wing panel is also a fairly reliable feature to identify Marsh Tit, but some Willow Tits can also lack this.
Lat/Lng: 50.9, -3.7
OS grid ref: SS8712